The present invention relates to display technology, and more particularly, to displays having a plurality of independently adjustable elements.
Most light-emitting devices exhibit a permanent, irreversible decrease in light output as the device is operated. These decreases are usually related to chemical or physical changes in the material that emits light. Emissive displays, such as organic light-emitting diodes (OLED), are constructed using numerous independent emissive pixels, each of which will undergo its own time-related output decay. When the display is used with static or repetitive images, frequently used pixels will exhibit significantly greater output decay than pixels used infrequently. This situation is known as xe2x80x9cdifferential agingxe2x80x9d. Pixels that are used frequently become dimmer than their unused neighbors. If the display image is then changed, the old image can sometimes be visible as a reduced brightness overlay on the new image. When past images become permanently incorporated into the display via differential aging, a xe2x80x9clatent imagexe2x80x9d is said to appear. Latent images can cause considerable distraction to a display user, and may impair correct interpretation of the displayed images. Since display usage cannot be predicted or controlled, some means must be utilized to prevent latent images from becoming visible. It is not possible to completely eliminate the differential aging mechanism, so other means must be found to compensate for the effect. The need to compensate for differential aging is particularly acute for OLED displays. Other display technologies, such as electroluminescent (EL) and cathode-ray tube (CRT) displays, may also benefit.
It is therefore an object of the invention to correct the effect of latent images on a display such that any present latent image is not visible to the user.
A feature of the invention is the compensation for differential aging by adjusting the output of individual emissive elements of the display, based upon past usage of each of the display elements.
An advantage of the invention is that periodic sampling and adjustment of individual display elements mitigates the effects of latent images, and the useful life of a display is thereby extended.
The invention provides a method of compensating for differential aging of independent emitters in a display. According to the method, an image on the display is periodically sampled to determine how often each independent emitter is used. A history is compiled of the use of each independent emitter for a predetermined time. The amount of luminance decay that each independent emitter has experienced over the predetermined time is estimated. The maximum luminance of each independent emitter is adjusted so that the maximum luminances of all of the independent emitters is substantially the same as the maximum luminance of the independent emitter that has experienced the most decay.
The invention also provides a method of reducing the visibility of latent images on a display, wherein the display has a plurality of independently controllable pixels, According to the method, a controller is attached to the display. The controller is configured to receive display image data. The controller controls the luminance of each pixel based on the desired image. The image data is periodically sampled to determine whether each pixel is being used. A usage history of each pixel, comprising the results of a plurality of periodic samples of the image data, is stored in a memory. After a predetermined number of samplings, the luminance decay of each pixel is estimated based on the usage history of each pixel. The luminance of each pixel is adjusted so that the luminances of the plurality of pixels appear to have equal age-related decay.
The invention also provides a display control system that reduces the visibility of latent images on a display. The display has a plurality of independently controllable pixels. A controller is configured to receive periodic inputs that are representative of the use of each pixel. A memory is connected to the controller and is configured to store the periodic inputs as a usage history of each pixel. A processor is connected to the controller and estimates the luminance decay of each pixel based on the usage history for each pixel. The controller adjusts the luminance of each pixel so that the luminances of all of the plurality of pixels appear to have equal age-related decay.